1. Field of the Invention
The present invention relates to a fixed constant velocity universal joint. Constant velocity universal joints are components of power transmission systems in motor vehicles and various industrial machines, intended to couple a rotational shaft on the driving side and a rotational shaft on the driven side for the sake of torque transmission at constant angular velocity. The constant velocity universal joints are divided into fixed type and slide type. The slide type allows both an angular displacement and an axial displacement while the fixed type allows an angular displacement alone.
2. Description of the Related Art
When a fixed constant velocity universal joint forms an angle, there occurs a force in the bending direction. Take, for example, a fixed constant velocity universal joint on the drive shaft of a front-wheel drive car. In steering the car, an outer ring fixed to the front axle forms an angle. The joint then forms the angle while pushing torque transmission balls held between track grooves of the outer ring and track grooves of an inner ring, and a cage retaining the torque transmission balls. Here, rolling and sliding frictions occur between the track grooves of the inner and outer rings and the torque transmission balls. Sliding frictions also occur between the inner spherical surface of the outer ring and the outer spherical surface of the cage, and between the outer spherical surface of the inner ring and the inner spherical surface of the cage. As a result, a reactive force arises in the direction opposite to the bending direction. This reactive force will be referred to as a bending direction load.
Conventionally, internal design specifications of a fixed constant velocity universal joint have been discussed with emphasis on joint functions, or strength and durability, alone. No consideration has been actively given to a reduction of the bending direction load, or an improvement in flexibility. At best, the bending direction load has been only checked for the actual value within the internal specifications for securing required strength and durability.
Excessive bending direction loads can hinder smooth joint movement, and in the case of a fixed constant velocity universal joint to be used with the drive shaft of a front-wheel drive car, give a sense of discomfort in steering operations. The lower flexibility also means that the fixed constant velocity universal joint cannot sufficiently absorb vibrations and forces to be absorbed by the formation of an angle, in which case the vibrations and forces might be transmitted to the car-body side through the shaft. Vibrations and forces can also enter in the opposite way, possibly affecting the NVH performance of the vehicle.